Synthesis and characterization of novel bis(diphenylphosphino)-oxalyl and (substituted) malonyl dihydrazones: P,N,N,P-tetradentate complexes of an oxalyl derivative with Cu(II), Pd(II), and Mn(II)

Novel ligands of bis(diphenylphosphino)-oxalyl, malonyl, and methyl- and ethyl-malonyl dihydrazones were synthesized by condensation of oxalyl, malonyl, methyl-malonyl, and ethyl-malonyl dihydrazide with o-(diphenylphosphino)benzaldehyde in different conditions. The dihydrazones exhibit three different tautomeric structures detected by NMR and IR spectra. The P-31 NMR spectrum demonstrates four different singlet signals, i.e., chemical shifts, of the three respective tautomers. Complexes of the oxalyl ligand with Pd2+, Cu2+, and Mn2+ ions are formed in 1:1 molar ratio. Their structures were characterized by IR, NMR, EPR, MS, EA, and TGA, in which the oxalyl ligand acts as a neutral P,N,N,P-tetradentate chelate. The pH stability of the complexes is in the region of ca. 4.5-7.5 and their activation energy was calculated from the conductivity measurements.